The condensation reaction of an olefin or a mixture of olefins over an acid catalyst to form higher molecular weight products is a widely used commercial process. This type of condensation reaction is known as an oligomerization reaction, and the products are low molecular weight oligomers which are formed by the condensation of up to 12, typically 2, 3 or 4, but up to 5, 6, 7, or even 8 olefin molecules with each other. Specifically, low molecular weight olefins, such as propene, 2-methylpropene, 1-butene and 2-butenes, pentenes and hexenes, can be converted by oligomerization over a zeolite catalyst or another suitable catalyst to a product which is comprised of oligomers and which is of value as a high-octane gasoline blending stock and as a starting material for the production of chemical intermediates and end-products. Such chemical intermediates and end-products include alcohols, acids, detergents and esters such as plasticizer esters and synthetic lubricants. Industrial oligomerization reactions are generally performed in a plurality of tubular or chamber reactors. Sulphated zirconia catalysts, liquid or solid phosphoric acid catalysts and sulphuric acid catalysts are also known catalysts for oligomerization.
Industrial hydrocarbon conversion processes employing zeolite catalysts typically run for several weeks before a catalyst change is required or a decommissioning of the reactor is needed. In industrial processes, the feeds for the reactions are generally obtained from refining activities such as a stream derived from catalytic or steam cracking, which may have been subjected to fractionation. The nature of the refining activities is such that there will be variations in the composition of the feed. In addition it may be desired to change the nature of the feed during a reactor run. However, these variations and changes may influence the activity and life of the catalyst and/or properties of the resulting products. Furthermore, the oligomerization reactions are exothermic and the size of the exotherm also depends upon the nature and amount of olefin present in the feed. Isobutylene and propylene are particularly reactive generating a large amount of heat per unit of mass reacting. This in turn may influence the performance of the catalyst and the characteristics of the products formed in the reaction.
Thus, in the prior art concerned with processes for the oligomerization of olefins, numerous approaches have been developed with regard to ensuring acceptable catalyst life and activity and controlling desired product characteristics.
For example, US-A-2007/0255081 (WO2005/058777) describes a process for the conversion of olefins in a reactor which process comprises continuously passing a feed comprising an olefin and water through a bed of catalyst under conversion conditions to form a conversion product, the water content of the feed being automatically controlled according to an analysis of the composition of the feed. Thus, the process of US-A-2007/0255081 adjusts the content of water in the feed as a means to control and optimize the process.
US-A-2012/0116141 (WO 2007/006398) describes a process for oligomerizing an olefin comprising contacting the olefin with a zeolite catalyst in a reactor tube of a tubular reactor having a shell that contains a temperature control fluid for removing heat of reaction from the reactor tube, in which process the olefin feed to the reactor contains at least 42 wt % of olefin, wherein operating conditions are controlled such that the reaction product mixture exiting the reactor is at a pressure of at least 55 barg and wherein the shell side temperature control fluid parameters are controlled such that the peak temperature in the reactor tube is no more than 50° C. above the temperature of the temperature control fluid as said fluid exits the reactor. Thus, the process of US-A-2012/0116141 uses a specific reactor design and temperature profile to control and optimize the process, in particular with regard to catalyst life and conversion achieved.
However, in view of the variations in the feed materials as noted above, there remains a need for providing further processes for the oligomerization of an olefin comprising contacting an olefin feed with an oligomerization catalyst under conditions suitable to oligomerize the olefin, which processes provide for alternative or further means for controlling and/or improving said type of process, in particular with regard to catalyst life and/or the desired composition of the products to be obtained.